1. Field of the Invention
The invention relates to a process and apparatus for the controlled release of metered quantities of finely divided solids with one or more venturi nozzles with regulated control for the purpose of applying lubricant or separating compounds to the stressed surfaces of pressing tolls in tablet making machines or for applying finely divided solids to solid carrier materials, particularly in the pharmaceutical, food or catalyst fields.
The aim of the invention is to release powdered or finely divided solids in controlled manner and in metered individual amounts, i.e., in the form of bundles of powder of a defined size, in fixed cycles onto carriers which are traveling past. The carriers might be, for example, in the food industry, baking molds or chocolates which are to be coated with a powdered material; in the pharmaceutical and catalyst field, tablets might be provided with separating coatings in this way; however, this process is particularly interesting for applying powdered lubricants to the mechanically stressed surfaces of pressing tools for making tablets out of granules if this lubricant has to be applied in controlled manner to specific zones of the pressing tools but also in specified quantities.
2. Description of the Prior Art
U.S. Pat. No. 4,323,530 describes a method of compressing granules to form tablets, cores for coated tablets and the like in which, before each pressing operation, a specific amount of lubricant in liquid or suspended form is applied to the stressed zones of the pressing tools using an intermittently operating nozzle system. This method of lubrication means that no lubricant such as magnesium stearate has to be added to the granules which are to be compressed; this results, for example, in drugs which have substantially improved bio-availability of the active substance contained therein. Since a lubricant, such as magnesium stearate, which is difficultly soluble in a solvent such as water or lower alcohol can only be applied to the pressing zones in the desired or necessary quantity if larger amounts of these solutions are sprayed or dotted onto the surfaces, the need has arisen for lubricants of this kind to be capable of being applied to the zones in question in powder form.
In this connection, a process was known (DE-A-2 456 298) for coating moulds for blanks by means of an air/lubricant mixture in which the lubricant was in the form of a dry powder so that it could be electrically charged so as to be deposited electrostatically in this state on the inner walls of a mould, using an injection device. The implementation of a process of this kind makes very stringent demands on the production of a suitable press. The electrostatic deposition also results in a high degree of contamination of the area surrounding the pressing tools as a result of unavoidable static charging both of the components and of the dust from the granules. This type of coating with lubricants has not caught on in the art of tablet manufacture for these and other reasons and differs fundamentally from a controlled application of lubricants to specific zones of the pressing tools and also to specific zones of carrier materials such as are conventionally used in pharmaceuticals, foods or catalysts.
U.S. Pat. No. 3,461,195 describes an apparatus for lubricating matrices using powdered lubricants. By means of a valve, compressed air is forced into a tank filled with the powdered lubricant and the mixture of powder and air is blown into a lubrication chamber on the tablet-making shoe. This apparatus is designed only for slowly operating eccentric presses and cannot be transferred to modern rotary presses.
Japanese Patent No. 20 103 73 describes the coating of the surfaces of pressing tools in tablet making machines with a mixture of powder and air. A cone of powder/air mixture is released at exit openings directed onto the pressing tools and the distribution of the mixture over the upper and lower punches is adjusted by means of a throttle valve. A strong current of air is needed to prevent blockages in the intake system and in the valve. Any clouds of the lubricant/air mixture in the region of the punches and dies which could result in contamination not only of the pressing tools and their sliding bearings but also of the tablet-making plate, are overcome by the provision of baffle plates and a suction device. The use of a cone of powder/air mixture for applying powdered lubricants to the pressing tools therefore requires extensive protective measures which are also difficult to carry out in the restricted space available between the lower and upper punches in a tablet making machine. Nevertheless, soiling of the tablet making machine in the long-term as a result of atomisation of the lubricant powder is unavoidable. According to the process of this Japanese patent, first of all a mixture of lubricant powder and air is produced, which is then passed to the exit openings, under the control of a valve, in order to be released there in the form of a spray cone; there is no discussion of any controlled and quantified application of the mixture of lubricant and air.